Rebecca Cooke failed in another medal bid but Britain's flagging fortunes were boosted elsewhere at the World Championships in Montreal.

Cooke trailed home seventh in the 800metres freestyle final but there was better news as Liam Tancock smashed his own 50m backstroke British record and Kate Haywood underlined her potential in the 50m breaststroke.

Cooke, who won bronze in the 800metres freestyle two years ago in Barcelona, was well off the pace as American Kate Ziegler took gold to add to her 1500m freestyle title earlier in the week.

"I felt completely shattered. I was taken out in the first 100m and then I had nothing, nothing at all," said Cooke. "I have been faster in training than I have ever been so I don't think it is due to fitness. It has not quite clicked, maybe there is something there I need to look at. It is quite hard to pinpoint what is wrong."

Tancock, 20, broke the first British record of the championships as he finished second in his 50m backstroke semi-final in a time of 25.22secs, bettering his previous best by nearly two tenths of a second.

He will now line up in the final after progressing as the second fastest qualifier behind Greece's Aristeidis Grigoriadis. The world record holder and reigning champion, Germany's Thomas Rupprath, was fourth fastest.

"I will be hoping to lower the British record again in the final and it would be great to get a medal," said Tancock.

"Team spirit here is pretty high. I am enjoying the team atmosphere, everyone is really getting behind each other.

"I am enjoying these championships and I am hopeful of bigger and better things to come. I am getting a lot out of the experience of racing with older and more specialist swimmers."

Grimsby's Haywood booked her place in the 50m breaststroke final after her semi-final time of 31.41secs guaranteed progression as the fifth fastest qualifier.

World record holder Zoe Baker, who competed for Great Britain before defecting to represent New Zealand last year, will line up against the Loughborough-based Haywood.

However, Australia's Jade Edmistone will be the one to beat after breaking the championship record in her semi-final.

Haywood said: "My aim was to make the final. I was fine out there and put my head together to go out and do what I did."

Australia's Danni Miatke won the women's 50m butterfly gold while South Africa's Roland Schoeman took the men's 50m freestyle final in a championship record time of 21.69secs.